In digital video and audio broadcast applications, packetized program information transmitted to a video decoder, such as a High Definition Television (HDTV) receiver, contains broadcast channels, e.g. Fox 5™, Channel 13™, from multiple broadcasters. The packetized program information of an individual broadcaster may contain the data content of several program sub-channels occupying the frequency spectrum previously occupied by a single analog broadcast channel. The sub-channels may comprise, for example, digital services including a main program channel, a financial service channel offering stock quotes, a sports news service channel and a shopping and interactive channel, all being conveyed within the 6 MHz bandwidth previously allocated to a single analog NTSC compatible broadcast channel.
The packetized program information of an individual broadcaster also contains ancillary information as well as the data content of the program sub-channels. The ancillary information includes system information and program specific data used in identifying and assembling packets comprising selected programs and also includes program guide and text information associated with the transmitted program data. In particular, the ancillary system information includes system timing information providing a time clock reference enabling determination of a time at which a specific program is to be broadcast. The ancillary program specific data may include program content rating information (such as PG-13 etc.) enabling parental control of viewing using a conditional access system such as a V-chip type system, for example. The ancillary system timing and content rating information is typically encoded along with program data to conform to the requirements of a known standard. One such standard detailing an information protocol incorporating system timing and content rating information for broadcast applications is entitled, Program and System Information Protocol for Terrestrial Broadcast and Cable, published by the Advanced Television Systems Committee (ATSC), 10 Nov. 1997, hereinafter referred to as the PSIP standard.
A number of problems may arise in a digital video system in processing system timing and program specific information from multiple broadcast sources. Specifically, problems arise in the use of the system timing information for scheduling program processing functions and for displaying a current time to a user. Problems also arise in providing a conditional access system that uses accurate program content rating information in authorizing access to programs whilst also providing desirable features such as the ability for a user to optionally override a previously set content rating limit. Thus there is a need to solve these problems and derivative problems.